Pressure Equalizing Device

ABSTRACT

The present invention relates to a pressure equalising device with a pressure equalising balloon, the volume of which is connected to a further volume, the pressure of which is intended to be kept at as constant a value as possible even in the event of an enforced change in volume. In order therefore to keep the cuff pressure within the pressure range that is generally considered to be useful and optimal of between approximately 20 mbar and 30 mbar, but also make possible, if required, to increase the pressure in a controlled manner, according to the invention the equalising balloon keeping the pressure generally constant is accommodated in a protective sleeve which has radial bulges deviating from a uniformly concave form matched to the outer contour of the balloon, which bulges are designed such that the equalising balloon first abuts against the wall areas of the protective sleeve matched to the contour of the balloon and then, when pressure is increased, extends only into the bulges, whereby the pressure in the equalising balloon gradually increases as the volume in the bulges increases.

The present invention concerns a pressure equalization device comprisinga pressure equalization balloon, wherein the volume of the pressureequalization balloon is connected to a further volume, the pressure ofwhich is to maintain a substantially constant value even in the event ofa forced change in volume at least within a predetermined volume rangeof the pressure equalization balloon.

Such a volume, the pressure of which is to maintain a value which is asconstant as possible even in the event of a change in volume imposedfrom the exterior, is for example the volume of the inflation cuff of arespiration cannula. The inflation cuff which in medical technicallanguage and hereinafter is also referred just as the “cuff” in thatcase surrounds a cannula introduced into the trachea (windpipe) of apatient and after insertion of the cannula is inflated to a low pressureof the order of magnitude of between 20 and 30 mbars so that it bearssealingly against the wall of the trachea, in that way fixes the cannulaand also prevents secretions which collect above the cuff in the areaaround the respiration cannula passing into the bronchial tubes or thelungs of the patient. Otherwise such secretions in which germs veryquickly multiply and which then pass into the deeper airways or thelungs lead to severe complications like for example lung inflammation.

A good sealing effect by such a cuff is of great significance inparticular in the case of patients undergoing long-term ventilation. Thecannula in that case can either be an endotracheal tube which isintroduced through the mouth and pharynx of the patient but it can alsoequally well be a tracheostomy cannula which is passed through asurgically produced opening (a tracheostoma) in the neck of a patientand thus connects the trachea to the ambient air or a ventilationdevice, by-passing the oral and pharyngeal cavity.

Particularly in the case of patients undergoing long-term ventilation inthat case the set cuff pressure is also of very great significance asthat pressure may not permanently exceed a pressure of 30 mbars becausethe pressure acting on the highly sensitive wall of the trachea can leadto impairment of blood circulation and as a result injury or woundsgoing as far as necrosis effects.

On the other hand the cuff pressure may also not be too low in order toprevent the above-mentioned secretion from passing the cuff. In additionair flowing uncontrolledly past the cuff could also trigger a falsealarm on a ventilation device as ventilation when using correspondingcannulas is basically to be effected by way of the lumen of the cannulaand is controlled on the basis of the flow of air through the cannula.

In order therefore to keep the cuff pressure in the pressure range whichis generally deemed to be appropriate and optimum of between about 20mbars and 30 mbars numerous devices have already been used and describedwhich are intended to keep the pressure in the cuff constant. In thatrespect it is to be borne in mind that the trachea cross-section canalso change due to a patient moving, turning or inclining the head andthus presses on the cuff in different ways and changes the volumethereof. The cuff therefore has to be connected to a suitable pressurereservoir by way of a suitable hose which is generally guided along thecannula or integrated into the wall of the cannula, which pressurereservoir can receive air or generally filling gas like for examplenitrogen from the cuff depending on the respective change in volume ofthe cuff and also return it to the cuff again in order to keep the cuffpressure at a constant value independently of a variation in the volumeof the cuff which possibly occurs.

For example electronic pressure regulators are known for that purpose,like also simple compensating volumes, in particular balloons, whereingenerally the pressure of a cuff is checked and adjusted by qualifiedmedical staff at certain time intervals, but often only once in a shift.

In addition a system is also already known, which operates with a latexballoon as a compensating volume, wherein the latex balloon has theproperty of maintaining a constant pressure at least within a certainrange of volume. In other words, a slight increase in the pressurealready leads to a corresponding increase in volume of the latex balloonwhile a slight reduction in pressure again leads to a reduction involume of the latex balloon so that as a result the pressure in a cuffconnected to a corresponding latex balloon remains at the sameapproximately constant value. To protect the very thin and delicatelatex balloon which has the desired properties, it is arranged in anexternal protective sheath or case which is preferably transparent,which is substantially spherical and which is sufficiently stable toprotect the balloon accommodated in the case in relation to shocks,damage or pressure exerted from the exterior, and it will be appreciatedthat the protective case must be air-permeable in order not to influenceexpansion or contraction of the equalization balloon within theprotective case.

Various apparatuses for keeping constant or monitoring the pressure ofcorresponding cuffs or cuff devices in the medical area are known fromU.S. Pat. Nos. 3,642,005 and 4,501,273, US patent application No2012/0090619 A1, EP 1 252 909 A2 and British patent GB 1 423 789.

Electronic pressure regulating systems are very complicated andexpensive. Balloon systems with very voluminous equalization balloonsare cumbersome to handle and involve the risk of damage to such aballoon. The known system with an equalization balloon of latex, whichis disposed within a stable transparent protective case, in principleoperates relatively well but suffers from the disadvantage that thelatex inter alia by virtue of its allergenic potential is undesirable orindeed unacceptable in many areas of medical treatment.

EP 1 252 909 A2 already describes a system comprising a main balloon(corresponding to the cuff) and a pilot balloon, wherein the mainballoon and the pilot balloon are to involve the same elasticity so thatthe condition or also in particular the pressure of the main balloon(cuff) can be read off on the basis of the condition of the visiblepilot balloon. In that respect EP 1 252 909 describes a material ofthermoplastic elastomers on a styrene base both for the main balloon andalso for the pilot balloon.

Even if the pressure in the cuff of a respiration cannula is generallyto be kept constant, there are situations in every day medicaloccurrences in which such a cuff is to be acted upon with a higherpressure deliberately and generally only for a short time, which higherpressure for example is between 30 and 50 mbars. That can scarcely beimplemented with the above-mentioned pressure equalization balloonswhich always further expand with an only slightly increasing pressure.It is admittedly known for such a balloon to be provided with a fixedprotective case which prevents further stretching beyond the volume ofthe protective case. This however means that the pressure suddenly risesvery greatly as soon as the equalization balloon has come to bearagainst the inside wall of the protective case. A well-controlledincrease to an only slightly increased pressure of for example betweenabout 30 and 50 mbars is in that case scarcely possible.

In comparison with that state of the art the object of the presentinvention is to provide a pressure compensation equalization devicewhich on the one hand keeps substantially constant a predeterminedpressure in another volume connected to the equalization balloon likefor example a cuff or a cuff device, but which also makes it possible toincrease the pressure in controlled fashion as required.

That object is attained in that the equalization balloon which keeps thepressure generally constant is accommodated in a protective case whichhas radial outward bulges deviating from a uniformly concave shapematched to the outside contour of the balloon, which bulges of such aconfiguration that the equalization balloon firstly bears against thewall regions of the protective case, that are matched to the contour ofthe balloon, and then upon an increase in pressure expands only into theoutward bulges, whereby the pressure in the equalization balloongradually increases with the increase in volume into the outward bulges.

It is desirable in that case if in the volume range of the equalizationballoon between the volume upon bearing against the regions matched tothe contour of the free balloon and the volume upon complete filling ofall outward bulges, it gradually rises and preferably approximately bythe factor of two.

The difference in volume between the volume upon bearing against theregions matched to the contour of the free balloon and the volume uponcomplete filling of all outward bulges should approximately be at least5% of the first-mentioned volume. The relative surface area proportionof the concave bulges 6 relative to the convex portions 5 a can be forexample between 20% and 70%.

In a preferred embodiment the equalization balloon is produced from athermoplastic polymer and prior to the first use was overstretchedbeyond the maximum intended regulating volume and was then relaxed tothe range of the regulating volume, as is described in the patentapplication filed at the same time to the same applicant and bearing thetitle “pressure equalization balloon and method for the productionthereof”.

Desirably a suitable equalization balloon is produced for use onrespiration cannulas, with an initial volume (prior to theoverstretching effect) of between about 3 and 8 cm³, which has increasedafter the first-time overstretching for example to a volume of betweenabout 200 cm³ (or even more), by between about 20 and 50%. Theregulating volume could then be in the range of for example between 10or 20 and 100 cm³, preferably in the range of between 30 and 70 cm³.

The present invention however is not limited to such a balloon ofthermoplastic polymers but can be applied to all kinds of balloons whichhave a suitable pressure characteristic, which firstly exhibits no oralmost no increase in pressure with increasing volume, but the pressureof which is to markedly increase as from a given volume.

The equalization balloon is enclosed by a protective case which protectsthe relatively delicate equalization balloon from external mechanicaleffects. Such a protective case, for example of stable transparentplastic material, is of a spherical basic shape with outward bulges oroutwardly shaped portions. The protective case can be for example of adiameter of the order of magnitude of between 50 and 60 mm.

As already mentioned a corresponding spherical protective case ofPlexiglas or any other suitable stable plastic material can be of adiameter of the order of magnitude of between 50 and 60 mm and thus of avolume of the order of magnitude of between 70 and 100 cm³. Theprotective case can possibly also be kept smaller and can be of adiameter of 40 mm and down to 30 mm or less. It will be appreciated thatthe corresponding protective case has at least one opening whichconnects the interior of the protective case to the environment in orderto always maintain the constant ambient pressure outside theequalization balloon so that the equalization balloon can expand andcontract unimpededly within the volume of the protective case.

It is however provided in that respect that the protective case,starting from its spherical basic shape, has some outward bulges whichare preferably arranged strip-like. That for example provides that theequalization balloon initially expands upon a slight increase inpressure until it bears against parts of the inside wall of theprotective case while thereafter further expansion of the equalizationballoon is possible only in the region of the outward bulges. Thatprovides a slight but markedly perceptible and visible increase inpressure until the outward bulges are also filled with the balloon,whereupon the pressure rises steeply upon a further feed of gas. In thetransitional range in which the balloon expands into the outward bulgeshowever a comparatively slight continuous rise in pressure is to benoted, which makes it possible to set in targeted and controlled fashiona higher cuff pressure which is desired at times. That is required forexample in some emergency situations if for example bleeding occurs inthe trachea or in the neck and pharynx cavity and has to be stoppedwithout the sealing contact of the cuff against the trachea wall beingabandoned but even has to be possibly increased.

A particular advantage of the use of thermoplastic polymers is that acorresponding balloon can be produced using an injection moldingprocess, which permits a very well controllable, uniform wall thickness,in which respect the wall thickness in turn is one of the parameters bywhich the specific regulating pressure can be set. A second parameterfor setting a regulating pressure involves the extent of theoverstretching effect.

Styrene-based thermoplastic polymers have proven to be particularlysuitable like for example SBS (styrene-butadiene-styrene), SIS(styrene-isoprene-styrene) and SEPS(styrene-ethylene-propylene-styrene). The material SEBS(styrene-ethylene-butylene-styrene) is particularly preferred for thepresent invention.

The thermoplastic material may also have fillers like for examplemineral oils and in particular medical white mineral oils.

Desirably the thermoplastic material is so selected or set that it has aShore 00 hardness (in accordance with ISO 868) of 30-70, preferably 50Shore 00. The tensile modulus at 100% stretching is typically in therange of between 40-150 kPa (in accordance with ISO 37).

The wall thickness of the pressure-less balloon prior to the first-offoverstretching, that is to say after the injection molding process, canbe for example in the range of between 0.4 and 1.5 mm. Upon stretchingof such a balloon and in particular for overstretching thereof apressure of the order of magnitude of between 40 and 60 mbars istypically required. If however the balloon is allowed to relax againafter adequate overstretching and to go back into the pressure-lesscondition then in that condition it is on the one hand of a generallysomewhat larger volume than after the injection molding operation, butin particular it has a different stretching characteristic, that is tosay the pressure which is required to inflate the balloon within theregulating volume range (typically less than a quarter of theoverstretching volume) is however only still at about half the pressurewhich is required for the first-time stretching and overstretching ofthe balloon and it remains substantially constant over a greater volumerange of the balloon. As stated the precise value can be relativelyaccurately set by specifically targeted choice of the wall thickness andby the controlled extent of the overstretching.

Admittedly the material occasionally has a certain “recovery effect” ifit was kept in the pressure-less condition for a prolonged period oftime, which has the result that, when being inflated again for the firsttime, the regulating pressure value has to be somewhat exceeded; ifhowever the available regulating volume (which for example is delimitedby the protective case) is once again completely put to use before theballoon is brought into operation then the desired stretchcharacteristic at the regulating pressure is very quickly restoredagain.

A further advantage of production by means of injection moldingprocesses is that the equalization balloon can be produced selectivelywith different wall thicknesses at various locations. In particular apreferred embodiment of the invention provides that the equalizationballoon has a reinforced opening ring which surrounds the balloonopening and whose wall thickness is at least 50% greater than the wallthickness of the balloon elsewhere and which accordingly does not takepart in the stretching effect upon pressure equalization. Such anopening ring can be produced with an accurately defined geometry andwall thickness so that for example it can be fitted directly on to asuitable standard connection (for example a Luer connector) in sealingengagement therewith.

The opening ring can in particular also have a peripherally extendingsealing flange which can be easily fixed to a suitable connectingportion of the connecting line to a cuff.

Corresponding standard connections are typically of a diameter in therange of between 12 and 25 mm.

The balloon should desirably be produced in such a way that the usableregulating volume includes the range of between 10 and 100 cm³,desirably the range of between 20 and 80 cm³. The maximum regulatingvolume is desirably delimited by a stable transparent outer protectivecase. In that way the balloon is visible in the interior of thetransparent case and the technical staff who operate the correspondingventilation apparatuses can directly see, on the basis of the conditionof the balloon, whether the pressure in the cuff is in the desiredrange.

Further advantages, features and possible uses of the present inventionwill be apparent from the following description of a preferredembodiment and the accompanying Figures in which:

FIG. 1 shows a perspective view in the left-hand part and a verticalsectional view in the right-hand part through an equalization balloonaccording to the invention in the pressure-less condition as is the casefor example immediately after production using an injection moldingprocess,

FIG. 2 shows a pressure equalization balloon in the inflated conditionas occurs during pressure regulation, wherein the contour of thepressure-less balloon is also indicated,

FIG. 3 shows a cross-section through the balloon of FIG. 2 correspondingto line III-III with a protective case additionally arranged around theballoon,

FIG. 4 shows a diagrammatic view of a further embodiment of the presentinvention,

FIG. 5 shows a sectional view of the FIG. 4 embodiment corresponding tothe section line V-V in FIG. 4, and

FIG. 6 shows a sectional view similar to FIG. 5 of a still furthermodified embodiment.

FIG. 1 shows a pressure equalization balloon 1 comprising a dome-shapedstretch portion 2, a cylindrical portion 3 of a somewhat greater wallthickness and finally a flange portion 4, the portions 3 and 4 formingan opening and connecting portion of the pressure equalization balloon1. For example the portions 3 and 4 can be fitted on to a Luer connectorwhich is typical in the medical area, that is to say a pipe connectionportion of a suitable diameter, wherein the free inside diameter of theportions 3 and 4 is preferably somewhat smaller than the outsidediameter of the tube connection portion on to which that connectingportion is fitted so that it bears under a slight elastic stresssealingly against the outside of the pipe connection portion. A clampingring or clamping band can also be arranged around the portion 3, whichsecurely holds the balloon fast to the pipe connection portion, with theflange portion 4 serving as a securing arrangement.

FIG. 2 shows the stretch portion 2 in a stretched condition, the stretchportion being identified in the stretched condition by reference to 2′.The contour of the unstretched portion 2 is also shown at the same time.The size relationships between the stretch portion 2′ in the stretchedcondition and in the pressure-less condition 2 approximatelyrealistically reproduce the size relationship in a typical regulatingrange in which the pressure in the interior of the equalization balloon2 remains substantially constant independently of the volume. In otherwords, a very slight increase in the pressure leads directly to acorresponding stretching of the portion 2′, which stretching reduces thepressure to the regulating value again. Conversely, a slight drop inpressure already leads to a reduction in the volume of the portion 2′ sothat the regulating pressure is then also restored.

FIG. 3 shows a particular embodiment of the present invention with aprotective sleeve or case 5 comprising a material which is relativelystrong and practically non-stretchable in comparison with the pressureequalization balloon 1 and which is preferably transparent so that it ispossible to see the actual condition of the pressure equalizationballoon 1 through the protective case 5.

In general the protective case 5 could be spherical with an openingportion corresponding to the connecting portion 3, 4 of the pressureequalization balloon 1 so that the stretch portion 2′, upon reaching aradius corresponding to the inside radius of the protective case, wouldbear over the full surface area against the inside wall of theprotective case so that, in the case of a further feed of gas into theinterior of the balloon, the pressure would rise immediately andsubstantially proportionally to the increase in the amount of gas.

The protective case 5 in FIG. 3 however deviates from a spherical shapeby virtue of the fact that it has strip-shaped outward bulges 6 whichstart from the lower opening region, as can be very clearly seen in thesectional view in FIG. 3, whereas the section perpendicularly to theplane of FIG. 3 would still substantially reproduce a spherical shape orfrom the inside a purely concave shape for the protective case 5. Theresult of that design configuration is that the stretch portion 2′,after reaching a radius corresponding to the radius of the convexportions of the protective case 5, bears against the inside wall 5 a ofthose convex portions, which in that region no longer allow furtherstretching of the portion 2′. Upon a further feed of gas or upon anincrease in the pressure therefore the stretch portion has to stretchout into the bulges 6. That limitation on the stretching of the portion2′ along the walls 5 a of the convex regions of the protective caseleads to a modified stretch/pressure characteristic in respect of thepressure equalization balloon 1 so that, after the balloon has reached avolume at which the stretch portion bears against the wall portions 5 a,the pressure upon a further feed of gas no longer remains constant butrises slightly linearly. In that way it is possible for the pressure tobe increased in a relatively controlled fashion from the normalregulating pressure, gradually and continuously, to a pressure as occursafter the bulges 6 are filled out by the parts of the stretch portion2′, which expand thereinto. That permits markedly easier adjustment of agiven pressure value between the regulating pressure and theabove-mentioned final pressure which can be for example approximatelytwice the regulating pressure. If therefore the regulating pressure isin the range of between 20 and 25 mbars the final pressure could bebetween 40 and 50 mbars, in which case that final pressure can be variedwithin relatively large ranges by a suitable configuration for thebulges 6 and the convex portions therebetween.

A correspondingly higher pressure in the cuff of a respiration cannulais required for example to stop bleeding or if certain treatments ortechnical measures are to be conducted on the patient or a respirationcannula, which are inevitably linked to greater movements of thecannula, in which case however the sealing integrity of the cuff in thetrachea is not to be impaired.

FIG. 4 diagrammatically shows a complete respiration system comprising arespiration cannula 7 with a cuff 6 and a pressure equalization balloonaccommodated in a spherical protective case 5′. The details of thisembodiment can be even better seen in the sectional view in FIG. 5. FIG.5 diagrammatically shows the respiration cannula 7, the cuff 6surrounding the cannula 7 and serving to seal off the intermediate spacebetween the wall of the trachea and the outside of the cannula 7, with afilling hose 9 connecting the interior of the cuff 6 to a pressureequalization balloon 2′, wherein in this case there is additionally alsoprovided a damping valve 10 in the filling hose 9 or the connectionthereof to the pressure equalization balloon 2′, which serves to dampthe possible flow of air or gas out of the cuff 6 into the equalizationballoon 2′. Upon artificial respiration and also upon spontaneousbreathing the pressure in the lungs and the trachea of the patientvaries, whereby in turn pressure is exerted from the exterior on thecuff 6, which pressure thereby urges air by way of the filling hose 9into the equalization balloon 2′. In that case there is a risk that thecuff 6 no longer bears sealingly against the wall of the trachea.

Instead the air or the filling gas should remain for somewhat longer inthe cuff 6, in which case a short-term increase in pressure is alsotolerated, so that during a respiration pressure peak the sealingintegrity of the contact between the cuff 6 and the wall of the trachearemains guaranteed. The damping valve 10 provides that the pressure inthe cuff 6 can be higher than the pressure in the equalization balloonat least for a short time, that is to say during correspondingrespiration pressure peaks. In the reversed direction however thedamping valve 10 is transmissive so that a drop in the pressure in thecuff 6 is immediately compensated. The valve 11 serves for filling thecuff and the equalization balloon with a predetermined amount of fillinggas (for example air or nitrogen).

In the respiration system according to the invention an alternative tothe damping valve 10 or a supplement thereto lies in a connecting hose 8between the cannula 7 and the protective case 5′, which in thisembodiment is also or can be spherical.

Respiration pressure peaks as occur both upon artificial respiration andalso in spontaneous respiration and which act on the cuff 6 from theexterior occur primarily in the interior of the respiration cannula 7 sothat the corresponding pressure peaks are also transmitted into theinterior of the protective case 5′ by way of the connecting hose 6 andthus also act on the equalization balloon 2′ from the exterior. Thesystem overall remains better in an equilibrium condition by virtue ofsimultaneous pressurization both of the equalization balloon 2′ and alsothe cuff 6 from the exterior.

It will be noted however that this means that the internal pressure inthe cuff additionally rises by the full pressure of a respiration airpeak. If therefore the respiration pressure is 20 mbars and the cuffpressure is also 20 mbars and the respiration pressure is transmittedinto the protective case 5′ by way of the connecting hose 8 the pressurein the pressure equalization balloon 2′ and also in the cuff 6 rises by20 mbars so that the cuff pressure is overall already 40 mbars, whichcould be unwanted in the long term.

In order to somewhat damp that effect the FIG. 6 embodiment alsoinvolves a modification to the effect that it is not the overall volumeof the protective case 5′ that is acted upon with the respirationpressure from the cannula 7, but only a further transmission balloon 12which is in contact only with a part of the surface of the pressureequalization balloon 2′ so that the pressure in the interior of theequalization balloon 2′ does not rise by the full value of therespiration pressure.

For the purposes of the original disclosure it is pointed out that allfeatures as can be seen by a man skilled in the art from the presentdescription, the drawings and the appended claims, even if they aredescribed in specific terms only in connection with certain otherfeatures, can be combined both individually and also in any combinationswith others of the features or groups of features disclosed hereininsofar as that has not been expressly excluded or technical aspectsmake such combinations impossible or meaningless. A comprehensiveexplicit representation of all conceivable combinations of features andemphasis of the independence of the individual features from each otheris dispensed with here only for the sake of brevity and readability ofthe description.

1. A pressure equalization device comprising a pressure equalizationballoon, whose volume is connected to a further volume, the pressure ofwhich is to maintain a value which is as constant as possible even inthe event of a forced change in volume, characterised in that theequalization balloon which keeps the pressure generally constant isaccommodated in a protective case which has radial outward bulgesdeviating from a uniformly concave shape matched to the outside contourof the balloon, which bulges of such a configuration that theequalization balloon firstly bears against wall regions of theprotective case, that are matched to the contour of the balloon, andthen upon an increase in pressure expands only into the outward bulges,whereby the pressure in the equalization balloon gradually increaseswith the increase in volume into the outward bulges.
 2. A pressureequalization device as set forth in claim 1 characterised in that theprotective case is of a spherical basic shape.
 3. A pressureequalization device as set forth in claim 1 characterised in that thevolume of the outward bulges of the protective case is at least 5% ofthe volume of the protective case without the outward bulges.
 4. Apressure equalization device as set forth in claim 1 characterised inthat the pressure equalization balloon comprises a styrene-basedthermoplastic elastomer.
 5. A pressure equalization device as set forthin claim 1 characterised in that the balloon is produced by injectionmolding.
 6. A pressure equalization device as set forth in claim 1characterised in that the wall thickness of the pressure-less balloonprior to the first-time overstretching is between 0.4 and 1.5 mm.
 7. Apressure equalization device as set forth in claim 1 characterised inthat the balloon has a reinforced opening ring which extends around aballoon opening and whose wall thickness is at least 50% greater thanthe wall thickness of the balloon elsewhere.
 8. A pressure equalizationdevice as set forth in claim 1 characterised in that the dimensions ofthe opening ring are matched to a standard connection of a diameter ofbetween 12 and 25 mm.
 9. A pressure equalization device as set forth inclaim 1 characterised in that the regulating volume includes the rangeof between 10 and 100 cm³.
 10. A pressure equalization device as setforth in claim 1 characterised in that the regulating volume includesthe range of between 20 and 80 cm³.
 11. A pressure equalization deviceas set forth in claim 1 characterised in that the balloon prior to thefirst use was subjected to an overstretching to a volume which is atleast four times the maximum regulating volume.
 12. A pressureequalization device as set forth in claim 1 characterised in that theballoon is set to a regulating value (target pressure range) of between20 and 30 mbars.
 13. A pressure equalization device as set forth inclaim 2 characterised in that the protective case has strip-shapedoutward bulges.
 14. A pressure equalization device as set forth in claim4 characterised in that the thermoplastic elastomer is SBS(styrene-butadiene-styrene).
 15. A pressure equalization device as setforth in claim 4 characterised in that the thermoplastic elastomer isSIS (styrene-isoprene-styrene).
 16. A pressure equalization device asset forth in claim 4 characterised in that the thermoplastic elastomeris SEPS (styrene-ethylene-propylene-styrene).
 17. A pressureequalization device as set forth in claim 4 characterised in that thethermoplastic elastomer is SEBS (styrene-ethylene-butylene-styrene).